辽宁早白垩世会鸟一新种(英文)

A NEW SPECIES OF THE BASAL BIRD SAPEORNIS FROM THE EARLY CRETACEOUS OF LIAONING,CHINA

记述了辽宁朝阳大平房早白垩世九佛堂组湖相地层中发现的会鸟化石一新种,窄脊会鸟(Sapeornis angustis sp.nov.)。尽管新种正型标本属于一亚成年个体,但除个体较小外,还在许多特征上很容易与属型种(朝阳会鸟)相区别。例如,不超过6枚荐椎,肱骨的三角脊和气窗均较细窄,三角脊远端的背突不显著尖锐,乌喙骨具有较长的肩峰突,叉骨枝较细,叉骨突较短,第一掌骨以及耻骨突均相对较短等。和始祖鸟以及其他已报道的会鸟标本一样,新种材料没有保存胸骨,肋骨上也未见钩状突起,推测这两种结构可能在个体发育的晚期才开始骨化,上述标本均为发育早中期的个体。会鸟新种的发现为这一基干的原始鸟类提供了新的解剖特征,并表明在会鸟的演化过程中存在个体的逐步增大以及一些形态特征的特化现象。这一新的发现还为分析早白垩世陆地生态系统的鸟类多样性增添了新的资料。

A new species of the avian Sapeornis is described based on a specimen discovered from the Early Cretaceous lacustrine Jiufotang Formation in Dapingfang, Chaoyang, Liaoning Province, Northeast China. The new species Sapeornis angustis is relatively small compared to the type species, S. chaoyangensis, and distinguishable from the latter in possessing 5-6 sacrals, a distinct narrow humeral deltopectoral crest with a less acute dorso-distal process, narrower furcular rami, a shorter hypocleidum, a relatively longer Metacarpal I and a shorter pubic symphysis. Like in Archaeopteryx and other known specimens of Sapeornis, the new species preserves no uncinate process or sternum, suggesting that both structures are ossified in a late stage of development and none of the known specimens of Archaeopteryx and Sapeornis is fully adult. The discovery of a new species of Sapeornis provides more anatomical information about this basal avian, and documents the trend of size increase and some morphological specializations in its evolutionary history. Furthermore, it also adds to our understanding of the differentiation and diversity of birds in the Early Cretaceous terrestrial ecosystem.